[MPlayer-users] Re: General video question so as to understand movie aspect

[Phil Bertram]

RC wrote:

> On Wed, 06 Sep 2006 07:23:25 +1200
> Phil Bertram <phil.bertram at clear.net.nz> wrote:
> 
>> Am I correct to assume that after I crop off the black bars and thus
>> have a movie that is 16/9 shape (crop=688:416:16:80), the movie is
>> still has an  aspect of 4/3 and so aspect I should use -aspect 4/3
>> when encoding with mencoder.
> 
> -aspect only affects the input, not the output.  For the output, you use
> "-lavcopts aspect=" to specify the aspect, or preferably  "-lavcopts
> autoaspect" to have it automatically calculate the proper aspect for
> you.

Ah yes. I see the error in my ways. I am still a little confused between
MOVIE aspect, which I believe we are dealing with here, and PIXEL aspect
which I think now may be a different concept.

Below is a the mplayer output from my test emcode using -lavcopts autoaspect 

If the movie is now at the correct aspect calculated by -lavcopts autoaspect
why is this movie scaled again at playback?

Eg.
Movie-Aspect is 1.76:1 - prescaling to correct movie aspect.
VO: [xv] 688x416 => 734x416 Planar YV12
                    ^^^^^^^

phil at pb:~$ mplayer test.avi
MPlayer dev-SVN-r19615-4.0.4 (C) 2000-2006 MPlayer Team
CPU: AMD Duron(tm) Processor (Family: 6, Model: 3, Stepping: 1)
CPUflags:  MMX: 1 MMX2: 1 3DNow: 1 3DNow2: 1 SSE: 0 SSE2: 0
Compiled for x86 CPU with extensions: MMX MMX2 3DNow 3DNowEx
Menu inited: /home/phil/.mplayer/menu.conf

Playing test.avi.

AVI file format detected.
VIDEO:  [FMP4]  688x416  24bpp  25.000 fps  1982.1 kbps (242.0 kbyte/s)
Clip info:
 Software: MEncoder dev-SVN-r19615-4.0.4
==========================================================================
Trying to force video codec driver family lavc...
Trying to force video codec driver family ffmpeg...
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
Selected video codec: [ffodivx] vfm: ffmpeg (FFmpeg MPEG-4)
==========================================================================
==========================================================================
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
AUDIO: 48000 Hz, 2 ch, s16le, 192.0 kbit/12.50% (ratio: 24000->192000)
Selected audio codec: [mp3] afm: mp3lib (mp3lib MPEG layer-2, layer-3)
==========================================================================
alsa-init: using device default
alsa: 48000 Hz/2 channels/4 bpf/65536 bytes buffer/Signed 16 bit Little
Endian
AO: [alsa] 48000Hz 2ch s16le (2 bytes per sample)
Starting playback...
VDec: vo config request - 688 x 416 (preferred colorspace: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.76:1 - prescaling to correct movie aspect.
VO: [xv] 688x416 => 734x416 Planar YV12
alsa-uninit: pcm closed-0.005 ct: -0.001 871/871 25%  5%  1.3% 9 0 20%

Exiting... (Quit)

> 
> The aspect of your output file will/should certainly not be 4/3.
> Croping, scaling, etc., changes the aspect ratio, and a new aspect has
> to be calculated.